1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a semiconductor device including a sensor configured to detect a direction of magnetism.
2. Description of the Related Art
A magnetic sensor technology has hitherto been known well in which a magnetic material, a magnetic flux concentrator, having a function of amplifying magnetism and a Hall element are combined. For example, in Japanese Patent No. 4936299, there is disclosed a technology relating to a sensor configured to detect a direction of a magnetic field that can detect a vertical magnetic field and a horizontal magnetic field. The sensor includes a magnetic flux concentrator formed on a surface of a semiconductor chip and having a flat shape, and a plurality of Hall elements. These Hall elements are arranged in an end portion region of the magnetic flux concentrator. Such a structure has an effect that magnetism in the Hall element region can be amplified.
FIG. 5 is a schematic view for illustrating a related-art magnetic sensor (see Japanese Patent Application Laid-open No. 2003-142752). The magnetic sensor includes a semiconductor substrate 1, Hall elements 2a and 2b, a protective layer 3, an underlayer metal layer 4, and a magnetic flux concentrator 5. The conventional art relates to a method of manufacturing a magnetic sensor that includes a magnetic flux concentrator having the function of amplifying magnetism and is configured to detect a magnetic flux that leaks from an end portion of the magnetic flux concentrator using the Hall elements. The underlayer metal layer 4 is formed above the semiconductor substrate 1 via the protective layer 3, and further, the magnetic flux concentrator 5 at a thickness of 15 μm having the function of amplifying magnetism is arranged on the underlayer metal layer 4. Such a manufacturing method has effects that a small magnetic sensor including Hall elements and a magnetic flux concentrator formed of a soft magnetic material can be manufactured with ease, and that the magnetic flux concentrator can be close to the Hall elements to realize a highly sensitive magnetic sensor.
FIG. 6 is a process flow diagram for illustrating a method of manufacturing a magnetic flux concentrator of a related-art magnetic sensor, in which a process of bonding a magnetic tape onto the semiconductor substrate 11 is illustrated. First, a wafer having ICs formed thereon is prepared. Then, the magnetic tape (amorphous metal tape) is bonded onto the wafer using an epoxy adhesive. Next, a magnetic flux concentrator pattern 14 is formed by photolithography. Then, the amorphous metal is etched. In this way, the magnetic flux concentrator is formed on the semiconductor substrate 11. The magnetic flux concentrator in this case has a thickness of 20 μm or more.
As described above, in the magnetic sensor illustrated in FIG. 5, the magnetic flux concentrator has a thickness of 15 μm or more. In the magnetic sensor illustrated in FIG. 6, the magnetic flux concentrator arranged on the semiconductor substrate 11 is formed using the magnetic tape at a thickness of 20 μm or more. When such a magnetic tape is used, the magnetic tape is bonded onto the semiconductor substrate 11 using an epoxy adhesive 12, and thus, there is a problem in that strong stress is applied to the Hall elements therebelow.
FIGS. 7A and 7B illustrate a magnetic sensor provided for the purpose of solving such a problem (see Japanese Patent No. 5064706). The magnetic sensor includes a semiconductor substrate 21 having a plurality of Hall elements 22a, 22b arranged therein, and a single magnetic material 23 (magnetic flux concentrator) having the function of amplifying magnetism that is arranged on a surface of the semiconductor substrate and that at least partly covers each of the Hall elements, the Hall elements being located in the vicinity of end portions of the magnetic flux concentrator. In the magnetic sensor, the magnetic flux concentrator is formed by electrolytic plating at a thickness of 6.1 μm to 14 μm. There is an effect that strong stress is prevented from being applied to the Hall elements to inhibit generation of an offset voltage due to a piezoelectric effect.
However, the technology disclosed in Japanese Patent No. 5064706 (see FIGS. 7A-7B) has a problem in that a small thickness of a magnetic material (magnetic flux concentrator) lowers the function of amplifying magnetism. Further, even though the magnetic flux concentrator has a small thickness, the magnetic material partly or entirely covers Hall elements, and thus, stress is generated. Hence, there is a problem in that generation of an offset voltage and the like due to a piezoelectric effect cannot be sufficiently inhibited. Further, elements other than the Hall elements are arranged as well below the magnetic material, and thus, change in characteristics thereof due to the stress in a similar way is another problem.